The present invention relates to pigment mixtures consisting of at least two components, component A being SiO2 flakes coated with one or more metal oxides and/or metals and component B being one or more coated or uncoated special-effect pigments, and to their use in varnishes, paints, printing inks, plastics and cosmetic formulations.
With platelet-shaped pigments, hiding power and gloss are often difficult to realize simultaneously to a satisfactory extent. For instance, SiO2 flakes or mica platelets covered with one or more thin metal oxide layers feature interference colours and a high lustre but at the same time, owing to the transparent substrate, feature high transparency and hence a comparatively poor hiding power.
Thus EP 0 562 329 discloses a pigment mixture comprising iron oxide-coated aluminium flakes in combination with iron oxide-coated mica pigments.
DE-A-42 40 511 discloses a pigment mixture which consists of an interference pigment and a platelet-shaped colour pigment. The interference pigment comprises metal oxide-coated mica flakes or SiO2 flakes, and the colour pigment can be coloured, uncoated SiO2 flakes. This pigment mixture is incorporated into coating materials, printing inks or plastics.
The object of the present invention is to provide a pigment mixture which is notable for relatively high hiding power and which lends itself well to incorporation into the respective system in which it is used, and for which at the same time a separation of pigment/colourant in the system is largely ruled out.
Surprisingly, a pigment mixture has now been found which has none of the disadvantages indicated above. The pigment mixture of the invention consists of at least two components, component A being SiO2 flakes coated with one or more metal oxides and/or metals and component B being one or more special-effect pigments. The admixture of the special-effect pigments to the coated SiO2 flakes is able to give the systems in which they are used a multiple flop, the colour effect is intensified, and new colour effects are achieved.
The invention thus provides a pigment mixture consisting of at least two components, component A being SiO2 flakes coated with one or more metal oxides and component B being one or more special-effect pigments.
The invention likewise provides the formulations, such as paints, varnishes, printing inks, plastics, agricultural films and cosmetic formulations, which comprise the pigment mixture of the invention.
The coated SiO2 flakes can be mixed in any proportion with the special-effect pigments. The ratio of component A to component B is preferably from 1:10 to 10:1, in particular from 3:1 to 5:1.
The SiO2 flakes preferably produced on a continuous belt in accordance with WO 93/08237 are based on a platelet-shaped, transparent matrix and generally possess a thickness of between 0.1 and 5 xcexcm, in particular between 0.2 and 2.0 xcexcm. The extent in the two other dimensions is usually between 1 and 250 xcexcm, preferably between 2 and 100 xcexcm and, in particular, between 5 and 40 xcexcm. The SiO2 flakes are provided with one or more metal oxide layers and/or metal layers. Examples of suitable metal oxides or metal oxide mixtures are titanium dioxide, zirconium oxide, zinc oxide, iron oxides and/or chromium oxide, especially TiO2 and/or Fe2O3. The SiO2 flakes can be coated as described, for example, in WO 93/08237 (wet chemical coating) or DE-A-196 14 637 (CVD process).
Instead of the outer metal oxide layer a semitransparent layer of metal can be used. Suitable metals for this are, for example, Cr, Ti, Mo, W, Al, Cu, Ag, Au and Ni. Prefered pigments have the following layer structure: SiO2 flakes+metal+SiO2+metal oxide.
To induce special colour effects, fine particles in the nanometre size range can be incorporated additionally into the metal oxide layers of high or low refractive index. Examples of suitable candidates are finely divided TiO2 or finely divided carbon (carbon black) with particle sizes in the range 10-250 nm. A controlled influence can be exerted on lustre and hiding power by virtue of the light-scattering properties of such particles. Preferably, the SiO2 flakes are coated with one or more metal oxides.
Suitable components B for the pigment mixture of the invention are all special-effect pigments familiar to the skilled worker in the effect pigment sector, examples being metal effect pigments, such as aluminium, copper, zinc, tin and their alloys. Aluminium and gold bronze alloys are preferably to be mentioned, especially those having a particle size of from 2 to 40 xcexcm. The pigment mixtures of the invention preferably comprise coated platelet-shaped iron oxide, aluminium flakes or coated aluminium flakes. Special-effect pigments of this kind are marketed by BASF under the name Paliocrom(copyright), by Eckart-Werke under the name Standard(copyright), and by the company Flex. Mention should also be made of pearl lustre pigments, Al2O3 flakes coated with metal oxides, such as TiO2 or Fe2O3, for example, graphite platelets, BiOCl or glass flakes.
Pearl lustre pigments, mica flake pigments coated with one or more metal oxides, are obtainable, for example, from Merck KGaA, Darmstadt, under the trade name Iriodin(copyright). The latter pigments are known, for example, from the German Patents and Patent Applications 14 67 468, 19 59 998, 20 09 566, 22 14 545, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602 and 32 53 017. Mica pigments coated with TiO2 and/or Fe2O3 are employed in particular. As phyllosilicate both natural and synthetic mica are suitable.
The pigment mixture of the invention is simple and easy to handle. The pigment mixture can be incorporated into the system in which it is used by simple stirring. Laborious milling and dispersing of the pigments is not necessary.
The pigment mixture of the invention can be used for pigmenting coating materials, printing inks, plastics, agricultural films, button pastes, for the coating of seed, for the colouring of food, coatings of medicaments or cosmetic formulations. The concentration of the pigment mixture in the system in which it is to be used for pigmenting is generally between 0.01 and 50% by weight, preferably between 0.1 and 5% by weight, based on the overall solids content of the system. This concentration is generally dependent on the specific application.
Plastics comprising the pigment mixture of the invention in amounts of from 0.1 to 50% by weight, in particular from 0.5 to 7% by weight, are frequently notable for a particular sparkle effect.
In the coating sector, especially in automotive finishing, the pigment mixture is employed in amounts of 0.5-10% by weight. The proportion in which the coated SiO2 flakes are mixed with component B, especially coated or uncoated aluminium flakes, depends on the desired effect. The SiO2 flakes are preferably employed with component B in a ratio of 5:1, in particular of 3:1.
In the coating material, the pigment mixture of the invention has the advantage that the desired colour flop effect is obtained by a single-layer coating (one-coat systems or as a basecoat in a two-coat system). This colour flop is extremely pronounced even under diffuse light. In comparison with coatings which comprise an intererence pigment rather than the coated SiO2 flakes, coatings with the pigment mixture of the invention exhibit a marked depth effect and a glitter effect and also a strong colour flop.
In the pigmentation of binder systems, for example for paints and printing inks for intaglio, offset or screen printing, pigment mixtures consisting of coated SiO2 flakes with Stapa(copyright)xe2x80x94aluminium and gold bronze pastes from Eckart-Werkexe2x80x94have proven particularly suitable. The pigment mixture is incorporated into the printing ink in amounts of 2-50% by weight, preferably 5-30% by weight and, in particular, 8-15% by weight. The mixing ratio of component A to component B is preferably in the range from 1:10 to 10:1. The printing inks comprising the pigment mixture of the invention exhibit purer hues and are of improved printability owing to the good viscosity values.
The invention likewise provides pigment preparations comprising coated or uncoated SiO2 flakes, metal effect pigments, binders and, if desired, additives, the said preparations being in the form of substantially solvent-free, free-flowing granules. Such granules contain up to 95% by weight of the pigment mixture. A pigment preparation in which the pigment mixture of the invention is pasted up with a binder and with water or an organic solvent, with or without additives, and the paste is subsequently dried and brought into a compact particulate form, e.g. granules, pellets, briquettes, a masterbatch or tablets, is particularly suitable as a precursor for printing inks.
The present invention therefore also provides formulations comprising the pigment mixture of the invention.
The examples which follow are intended to illustrate the invention without, however, limiting it.